If polar bears dream, perhaps they dream of pale blue ice, deep blue water.Perhaps they dream fat seals, good hunts--or they dream themselves all the way back to the snow den where they they were born.Polar bears cannot dream of what they have never seen, cotton fields, or factories manufacturing PVC, or other far-off works of men. For their part, the humans, the growers and the builders and the makers, scarcely think of the polar bear.He is so far away--and yet not far enough.

The by-products, the toxic chemical residues of human production, are not only at the polar bear’s door, but in the polar bear.

This has been known for some time. In 2006, the International Arctic Programme of the World Wildlife Fund published “Killing Them Softly. . . . Health Effects in Arctic Wildlife Linked to Chemical Exposures”--a meta-study combining research findings from many scientists. It reported the remote, seemingly pristine Arctic is deeply contaminated with agricultural and industrial chemicals. It spoke to the contamination of polar bears in particular--noting that chemical pollutants are concentrated in the polar bear’s super-high-fat, top-of-the-food chain diet. They are stored in the insulating layer of fat essential to the bears’ survival in the Arctic cold. They accumulate over the course of the polar bear’s long life--and they are passed to polar bear cubs in their mother’s milk (http://d2ouvy59p0dg6k.cloudfront.net/downloads/arctic_wildlife_health_effects_report_1___23_may.pdf).

In the polar bear is a mix of those man-made chemicals together called POPs, or Persistent Organic Pollutants. These, according to the United Nations Environment Programme (UNEP) have in common that they are toxic, they linger in the environment for years, and they circulate globally, moving great distances, in large part through a repeated cycle of evaporation, then precipitation. UNEP confirms that POPs are “lipophilic”--that is, they build up in the fatty tissue of living animals--and notes that in these tissues, concentrations of POPs can biomagnify to levels “up to 70,000 times higher than the background levels” (http://www.cep.unep.org/publications-and-resources/marine-and-coastal-issues-links/persistent-organic-pollutants-pops-and-pesticides).

What does this mean for the unsuspecting polar bear? The National Oceanic and Atmospheric Administration, or NOAA, reports that Persistent Organic Pollutants in the Arctic, intensely concentrated at the top of the food chain, are known in mammals to impair sexual development, undermine reproductive health, damage the immune system, interfere with liver function, and open animals to a higher risk of developing tumors (http://www.arctic.noaa.gov/essay_calder.html).

Ongoing research focuses on the impacts of environmental pollution on wildlife. This specialized study, called “veterinary ecotoxicology,”has occupied Dr. Christian Sonne since 1999. A senior research scientist at Aarhus University in Denmark, Sonne teaches at the university’s Center for Arctic Environmental Medicine http://pure.au.dk/portal/en/persons/christian-sonne(d9d824ac-a413-4a2a-bfbf-aff2aa7d406a)/cv.html?id=51902397) His work has thrown light on one potential cost, to polar bears, of chemical contamination. Sonne and his colleagues believe a complex of POPs known to be endocrine-system disruptors have steeply raised the threat of reproductive failure for polar bears, presenting a “serious challenge to the species’ survival” (http://www.ncbi.nlm.nih.gov/pubmed/25601730).

The East Greenland study looked at 75 polar bears, all from the same subpopulation (http://pubs.acs.org/doi/abs/10.1021/es060836n). Newly-published research is more expansive, taking in evidence from 279 bears representing eight subpopulations. Here lead author Sonne and eight fellow scientists find that exposure to endocrine-disrupting POPs is linked to changes in the polar bear’s penile bone, indispensable to his successful mating.In contaminated bears, this bone is less dense than ordinary, and more prone to fracture.Brittle penis bones threaten “fertilization failure”--according to this new study, now rivaling climate change as a block to the future of polar bears (http://www.ncbi.nlm.nih.gov/pubmed/25601730).

These beautiful giants have survived millennia, adapted superbly, emerged as natural kings of one of the most remote and forbidding regions of the earth.They have no enemies but us.We never dreamt of doing it, but we have pushed them toward the edge.

In our defense, it must be said we became the enemies of polar bears by accident.When we bristled the face of the planet with smokestacks, we hardly guessed we were a threat to the sky.When we invented and manufactured the synthetic agricultural and industrial chemicals that emerged as POPs (including pesticides and fertilizers, fire-retardants, lubricants, plasticizers, hydraulic fluids) we imagined we were improving the world. Alas.

However, we know more now. For polar bears and for the planet, for each other, now we can do better.